During one process to manufacture a semiconductor device, an electrically conductive adhesive such as epoxy paste or metal is placed on a paddle of a lead frame. A back side of a semiconductor die having a front (circuit) side with bond pads and back side opposite the front side is adhered to the paddle of a lead frame with the conductive material. Other materials used to attach a die to a paddle include conductive and nonconductive materials such as epoxy film, epoxy film on tape, glue, and thermoset and/or thermoplastic-coated polyimide.
Other attachments of a die to a lead frame are described in U.S. Pat. Nos. 5,140,404 and 5,177,032 by Fogal, et al.; U.S. Pat. No. 5,218,229 by Farnworth; and U.S. Pat. Nos. 5,256,598 and 5,304,842 by Farnworth et al.; each of which is assigned to Micron Technology, Inc. and incorporated herein by reference.
Another semiconductor assembly is a leads-over-chip (LOC) assembly. In one typical leads-over-chip (LOC) application, a polyimide carrier material is manufactured having a thermoset epoxy adhesive or a polyimide-type adhesive coated on either side. The carrier is interposed between the lead frame and a circuit side of the semiconductor die, then the adhesive is cured with heat thereby securing the die to the lead frame.
During shipment of the lead frame from the manufacturer to the user the manufacturer secures fingers and leads of the lead frame to ensure they are not bent during shipping. The fingers and leads are secured with a lead lock tape which is left in place during device processing. The lead lock tape conventionally comprises a polyimide carrier film which is a lower grade material compared to the LOC adhesive tape carrier film, and is less expensive. The lead lock tape is coated on one side with a butyl rubber thermoset adhesive which secures the tape to the lead frame and prevents the leads from moving or bending during shipping.
Current LOC assemblies have various problems. For example, the nonconductive adhesive attachment between the die and the lead frame is relatively expensive because of the cost of the thermoplastic polyimide adhesive which must be coated on both sides of the carrier film. Further, a dedicated tape dispensing tool and a heating block are required which add expense and manufacturing steps to the manufacturing process. The thermoplastic which attaches the die and the lead frame to the carrier requires relatively high melt temperatures, for example in the range of 300.degree. C. to 450.degree. C. which stresses the die and the circuitry thereon. Thermoset tapes require somewhat lower temperatures, for example in the range of from about 200.degree. C. to 300.degree. C.
A method and structure for die attach which has advantages over current methods and structures would be desirable.